Electrochemical Incineration of 4-Chlorophenol and the Identification of Products and Intermediates by Mass Spectrometry

Abstract

This report summarizes results obtained as part of a larger effort to demonstrate the applicability of electrolytic procedures for the direct anodic (oxidative) degradation of toxic organic wastes. We refer to this process as "electrochemical incineration" (ECI) because the ultimate degradation products, e.g., carbon dioxide, are equivalent to those achieved by thermal incineration processes. In this work, the ECI of 4-chlorophenol is achieved in an aqueous medium using a platinum anode coated with a quaternary metal oxide film containing Ti, Ru, Sn, and Sb oxides. The electrode is stable and active when used with a solid Nafion membrane without the addition of soluble supporting electrolyte. Liquid chromatography (LC), including reverse phase and ion exchange chromatography, is coupled with electrospray mass spectrometry (ES-MS) and used, along with gas chromatography-mass spectrometry (GC-MS) and measurements of pH, chemical oxygen demand (COD), and total organic carbon (TOC), to study the reaction and identify the intermediate products from the ECI of 4-chlorophenol. Twenty-six intermediate products are identified and reported. The most abundant of these products are benzoquinone, 4-chlorocatechol, maleic acid, succinic acid, malonic acid, and the inorganic anions chloride, chlorate, and perchlorate. After 24 h of ECI, a solution that initially contained 108 ppm 4-chlorophenol yields only 1 ppm TOC with 98% of the original chlorine remaining in the specified inorganic forms. LC-ES-MS and direct infusion ES-MS detection limits are between 80 ppb and 4 ppm for these intermediate products. Elemental analysis of the electrolyzed solutions by inductively coupled plasma mass spectrometry ICP-MS showed that only trace amounts (<25 ppb) of the metallic elements comprising the metal oxide film were present in the solution.

Application of BDD thin film electrode for electrochemical decomposition of heterogeneous aromatic compounds

“…Electrochemical conversion and combustion seem to be environmentally friendly, because the only reagent used is electrical current, pH is neutral and mineralization is more extended than, for example, in the Fenton process. In general, electrodes for the oxidation of organic pollutants can be made from numerous materials [4][5][6][7]. However, for wide application of electrochemical degradation it is necessary to optimize electrolysis conditions, e.g.…”

Analytical methods in photoelectrochemical treatment of phenol

“…Moreover Johnson et al 32 demonstrated that phenol was degraded into intermediate compounds (benzoquinone and carboxylic acids) during the photoelectrochemical degradation. They observed that the solution color changed to light brown with benzoquinone generation and returned to its original colorless appearance with the gradual conversion of this substance into carboxylic acids.…”

Advanced Oxidation Processes (AOPs) for Removal of Pesticides from Aqueous Media

“…The most useful direct electrochemical method is anodic oxidation (Kaba et al, 1990;Kotz et al, 1991;Stucki et al, 1991;Comninellis andPulgarin, 1991, 1993;Murphy et al, 1992;Comninellis and Nerini, 1995;Feng et al, 1995;Johnson et al, 1999;Gandini et al, 2000;Rodrigo et al, 2001;Rodgers and Bunce, 2001;Wu and Zhou, 2001) where organic compounds are essentially degraded by reaction with adsorbed hydroxyl radicals at the anode surface, which are generated from water oxidation:…”

“…Thus, although the traditional Pt anodes has been used for this purpose (Kaba et al, 1990;Kotz et al, 1991;Stucki et al, 1991;Comninellis andPulgarin, 1991, 1993;Murphy et al, 1992;Comninellis and Nerini, 1995), it are less efficient that the oxide-base electrodes such as PbO 2 (Kaba et al, 1990;Feng et al, 1995;Wu and Zhou, 2001), doped PbO 2 (Feng et al, 1995), doped SnO 2 Stucki et al, 1991;Comninellis andPulgarin, 1991, 1993;Johnson et al, 1999), IrO 2 (Comninellis and Nerini, 1995;Rodgers and Bunce, 2001) or more recently to the boron-doped diamond thin-layer anode, BDD (Gandini et al, 2000;Rodrigo et al, 2001). On the other hand, the indirect electrochemical methods involves the previous formation of oxidizing agents such as H 2 O 2 (Hsiao and Nobe, 1993;Do 1993Do , 1994Ponce de Leon and Pletcher, 1995;Brilla et al, 1996;Brillas et al, 1998;Alvarez-Gallegos and Pletcher, 1999;Harrington and Pletcher, 1999;Brillas et al, 2000;Oturan et al, 2000, Oturan, 2000Oturan et al, 2001):…”